Low dielectric materials

ABSTRACT

The invention provides a low dielectric material. The low dielectric material comprises: (i) 5-50 parts by weight of polyphenylene ether (PPE) resin having a Mw of 1000˜7000, a Mn of 1000-4000 and Mw/Mn=1.0-1.8; and (ii) 10-90 parts by weight of liquid crystal polymer with allyl group having a Mw of 1000˜5000, a Mn of 1000-4000 and Mw/Mn=1.0-1.8, wherein the dielectric material has Dk of 3.4-4.0 and Df of 0.0025-0.0050. The dielectric material is suitably used in prepregs and insulation layers of a circuit board, because it has high Tg, low thermal expansion coefficient, low moisture absorption and excellent dielectric properties such as Dk and Df.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a Continuation-in-Part of co-pending application Ser. No. 13/845,908, filed on Mar. 18, 2013. The entire contents of which are hereby incorporated by reference.

BACKGROUND OF THE INVENTION

1. Technical Field

The invention relates to a material with low dielectric loss, particularly to a resin composition.

2. Related Art

As developed with wireless transmission products and technologies of transmitting high frequency, epoxy resin and novolak resin cannot satisfied for the advance application, especially high frequency printed circuit board (PCB). Fluorine-containing resin can be used as PCB with low dielectric loss. However, fluorine-containing resin is expensive and not easy to work, and thus limited to the use of military and astrodynamics. In addition, polyphenylene ether (PPE) resin has excellent mechanical property and dielectric property such as Dk and Df. Therefore, the PPE resin is preferable to be used a material for high frequency PCB.

However, because the PPE resin is a thermal plastic resin, as applied in a copper-clad laminate, it may has disadvantages as follows: it is not easy to work due to a high melting viscosity of PPE resin, interlayer film is easy released in a solvent clean step during a process for manufacturing PCB due to a poor solvent resistance of PPE resin, and it is not easy to operate above a temperature of 250° C. in soldering process due to melting point close to Tg. Therefore, PPE resin has to be modified by curing so as to meet the requirement of using in PCB.

Curing modification of PPE resin generally has two manners: PPE resin may become curable resin by introducing crosslinking active functional groups to molecular structure of PPE resin. Alternatively, PPE resin may become co-mixing curable composite material by introducing other curable resins to molecular structure of PPE resin with co-mixing modification or interpenetrating network technology. However, PPE resin is likely incompatible with the active functional groups or curable resins, because the polar difference exists in their chemical structures. Alternatively, PPE resin may lose the excellent properties, after it conducts curing modification with the active functional groups or curable resins.

Therefore, there is a need to develop a material has excellent dielectric properties and other properties such as high Tg, low coefficient of thermal expansion and low water absorption of PCB requirement. Also, the material can be applied in the manufacture of high frequency PCB.

SUMMARY OF THE INVENTION

An object of the invention is to provide a low dielectric material, which has excellent dielectric properties, low coefficient of thermal expansion and low water absorption.

To accomplish the above object, there is provided a low dielectric material, which comprises: (i) 5-50 parts by weight of polyphenylene ether (PPE) resin having a Mw of 1000˜7000, a Mn of 1000-4000 and Mw/Mn=1.0-1.8; and (ii) 10-90 parts by weight of liquid crystal polymer with allyl group having a Mw of 1000˜5000, a Mn of 1000-4000 and Mw/Mn=1.0-1.8, wherein the dielectric material has Dk of 3.4-4.0 and Df of 0.0025-0.0050.

In the low dielectric material of the invention, the low dielectric material further comprises 0.01-15 parts by weight of bismaleimide resins. In the low dielectric material of the invention, the low dielectric material further comprises 0.01-10 parts by weight of polymer additives.

In the low dielectric material of the invention, the polyphenylene ether resin is represented by the formula

wherein Y represents at least one C, O and benzene ring or the combination.

In the low dielectric material of the invention, bismaleimide resins are selected from groups consisting of

Phenylmethane maleimide

wherein n≧1;

Bisphenol A diphenyl ether bismaleimide

3,3′-dimethyl-5,5′-diethyl-4,4′-diphenylethane bismaleimide

and

1,6-bismaleimide-(2,2,4-trimethyl)hexane.

In the low dielectric material of the invention, the polymer additives are selected from groups consisting of

Homopolymers of Butadiene

wherein y=70% and x+z=30%;

Random copolymers of butadiene and styrene

wherein y=30%, x+z=70% and w=≧1, and the amount of styrene=25 wt %;

Maleinized Polybutadiene

wherein y=28% and x+z=72%, the amount of maleic anhydride=8 wt %;

Butadiene-styrene-divinylbenzene copolymer; and

Styrene Maleic Anhydride copolymer

wherein X=1˜8 and n≧1.

In the low dielectric material of the invention, it is preferable that crosslinking agent is added to increase crosslinking density of resins. The crosslinking agents with 40-80 parts by weight may be selected from the following groups consisting of

In the low dielectric material of the invention, it is preferable that catalyst is added to increase reaction of crosslinking agents and other resins. The catalysts includes at least one peroxide having 116° C.-128° C. for a half life of 10 hours with 2-8 phr based on the total weight of PPE, BMI, polymer additives and crosslinking agents. The suitable peroxides comprise dicumyl peroxide, α,α′-bis(tert-butylperoxy)diisopropyl benzene and 2,5-di(tert-butylperoxy)-2,5-dimethyl-3-hexyne.

In the low dielectric material of the invention, it is preferable that filler is added to increase thermal conductivity and mechanical strength, and reduce thermal expansion. The suitable fillers may be fused silica, sphere-shaped silica, talc aluminum silicate and soft silica, e.g., siliesoft, wherein the soft silica can be used to reduce a drill bit wearing away when PCB is drilled to form holes by the drill bit. The soft silica has a particle size in a range of 0.5 μm-10 μm.

In order to increase flame retardation of the low dielectric material of the invention, halogen-containing flame retardants and flame retardants without halogen may be used. The halogen-containing flame retardants may comprise decabromodiphenyl ethane. The flame retardants without halogen may comprise phosphor-containing flame retardants and phosphates. The phosphor-containing flame retardants and phosphates are produced by ALBEMARLE CO., LTD. The phosphates are like tetrakis(2,6-dimethylphenyl) 1,3-phenylene bisphosphate, HCA derivative (I), HCA derivative (II) and HCA derivative (III). The tetrakis(2,6-dimethylphenyl) 1,3-phenylene bisphosphate can be represented by the formula, [OC₆H₃(CH₃)₂]₂P(O)OC₅H₄OP(O)[OC₆H₃(CH₃)₂]₂;

HCA derivative (I) having the following paradiphenyl phosphoryl dibenzyl structure:

HCA derivative (II) having the following structure:

wherein with the proviso that when B is —CH₂—, —CH(CH₃)—, m is 1 and n is 1 to 3; with the proviso that when B is ═CHCH═, m=2 and n=0; and

HCA derivative (III) having the following structure (XP7866, Albemarle):

wherein A is a direct bond, C₆-C₁₂ aryl, C₃-C₁₂ cycloalkyl, or a C₃-C₁₂ cycloalkenyl, wherein said cycloalkyl or cycloalkenyl may be optionally substituted by a C₁-C₆ alkyl;

-   each R¹, R², R³ and R⁴ are independently hydrogen, C₁-C₁₅ alkyl,     C₆-C₁₂ aryl, C₇-C₁₅ aralkyl or C₇-C₁₅ alkaryl; or R¹ and R² or R³     and R⁴ taken together can form a saturated or unsaturated cyclic     ring, wherein said saturated or unsaturated cyclic ring may be     optional substituted by a C₁-C₆ alkyl; -   each m is independently 1, 2, 3 or 4 -   each R⁵ and R⁶ are independently hydrogen or a C₁-C₆ alkyl; -   each n is independently 0, 1, 2, 3, 4 or 5; -   with the proviso that when A is aryl or a direct bond, n cannot be     0.

The foregoing and other objects, features and advantages of the present invention will be apparent to those skilled in the art from the following detailed description.

BRIEF DESCRIPTION OF THE DRAWINGS

The features of the invention believed to be novel are set forth with particularity in the appended claims. The invention itself, however, may be best understood by reference to the following detailed description of the invention, which describes an exemplary embodiment of the invention, taken in conjunction with the accompanying drawings, in which:

The FIGURE shows a FTIR spectrum of liquid crystal polymer of an embodiment according to the present invention.

DETAILED DESCRIPTION OF THE INVENTION

In one aspect of the present invention, there is provided a thermal curable dielectric material to produce a prepreg in a successive process in the following examples 4-1 to 4-7. The process uses the dielectric material as a coating on a substrate which may be a fiberglass cloth. The apparatus for producing the prepreg includes a pasting tank wherein there are provided a plurality of rolls. The pasting tank is filled with the dielectric material. A roll of fiberglass cloth may enter the pasting tank and pass the plurality of rolls. The fiberglass cloth is sufficiently impregnated with the dielectric material, and then surplus dielectric material is removed by a metering roller. A heat treatment for curing the dielectric material and removing the solvent is required at 100° C. to 350° C. for 1 minute to 5 hours, preferably at 150° C. to 300° C. for 1 minute to 3 hours. The prepreg is obtained after the cured dielectric material is cooled down and the fiberglass cloth is wrapped.

A double-sided copper-clad laminate is produced by providing several prepregs in a neat stack between two electrodeposited copper foils, conducting a hot pressing process under 40 to 900 psi, raising temperature from 80° C. to 200° C. in 30 minutes, and then hot pressing at 200° C. for 120 minutes, and then cooling down to room temperature in 30 minutes in a vacuum pressing machine. The prepreg includes a fiberglass cloth of electrical grade 2116 and the dielectric material. Generally, a double-sided copper-clad laminate with a thickness of 1.0 mm is produced by providing 4 sheets of prepregs in a neat stack between two electrodeposited copper foils, with a thickness of 1.5 mm is produced by providing 7 sheets of prepregs, and with a thickness of 2.0 mm is produced by providing 10 sheets of prepregs.

The low dielectric material of the present invention may form a stable homogeneous solution in a solvent with a low boiling point. The properties of a copper-clad laminate with the dielectric material of the invention were determined including Tg, heat decomposition temperature, heat decomposition time, solder heat resistance (288° C.), thermal expansion coefficient, water absorption, thermal conductivity, dielectric constant, dielectric loss tangent and flammability according to IPC-TM-650 test method manual. The determining results show the copper-clad laminate with the dielectric material of the invention has high Tg, excellent dielectric properties such as Dk and Df, low water absorption, high thermal resistance and high thermal conductivity. The copper-clad laminate is suitable used as a substrate for electronic elements and IC package.

EXAMPLES

TABLE 1-1 INFLUENCE OF PPE RESIN AMOUNT AMOUNT OF PPE RESIN EXAMPLE 4-1-1 C1 C2 C3 C4 C5 C6 C7 PPE resin SA9000 60 52.5 45 41 37.5 34 22.5 BMI resin 5100 15 15 15 15 15 15 15 Polybutadiene Ricon100 10 10 10 10 10 10 10 Crosslinking TAIC 15 22.5 30 34 37.5 41 52.5 agents Flame XP7866, phr 20 20 20 20 20 20 20 retardants fillers Fused silica, 20 20 20 20 20 20 20 phr catalysts Peroxide 2.5 2.5 2.5 2.5 2.5 2.5 2.5 119° C. for a half life of 10 hrs Tg, TMA IPC-TM-650 206 224 229 221 212 213 212 2.4.24.3 coefficient of IPC-TM-650 58/334 60/305 56/251 53/247 56/211 61/204 55/245 thermal 2.4.24 expansion (α1/α2), ppm/ ° C. water PCT/121° C./ 0.29 0.33 0.34 0.34 0.39 0.39 0.40 absorption 1 hr 288° C. Dip288° C. >600 >600 >600 >600 >600 >600 >600 thermal resistance Dk(2-10 GHz) Cavity 3.93 3.89 3.89 3.89 3.90 3.86 3.87 Df(2-10 GHz) Cavity 0.0057 0.0054 0.0048 0.0044 0.0040 0.0040 0.0039 flammability UL94 V-0 V-0 V-0 V-0 V-0 V-0 V-0

Tg, Dk and Df were compared with different ratio and amount of PPE. The Tg level may be affected by the amount of PPE used. Also, the amount of PPE may also have an effect on the Dk and Df value. When the amount of PPE is high, Dk and Df may be high. When the amount of PPE is low, Dk and Df may be low. Typically, a low value for the Dk and Df is preferred. In addition, the thermal expansion coefficient may be raised when PPE is added, and BMI is added to balance the effect. In Table 1-1, part number SA9000 of PPE with chemical name of Polyphenylene Oxide (PPO) or Polyphenylene Ether (PPE) is produced by Sabic CO., LTD.

TABLE 1-2 INFLUENCE OF LCP AMOUNT AMOUNT OF LCP EXAMPLE 4-1-2 C8 C9 C10 C11 C12 C13 PPE resin SA9000 48.5 27 5.4 13.5 13.5 13.5 BMI resin 5100 0 0 0 15 15 15 Polybutadiene Ricon100 0 0 0 10 10 10 LCP — 10 50 90 50 50 50 Crosslinking TAIC 41.5 23 4.6 11.5 11.5 11.5 agents Flame HCA derivative (II), 0 0 0 0 27 27 retardants phr Decabromodiphenyl 11 14 18 12 0 0 Ethane, phr fillers Fused silica, phr 20 20 20 20 20 20 catalysts Peroxide 119° C. for 2.5 2.5 2.5 2.5 2.5 2.5 a half life of 10 hrs Imidozole, phr 0.1 0.5 0.9 0.5 0.5 0.5 Tg, TMA, ° C. IPC-TM-650 193 219 205 225 230 227 2.4.24.3 coefficient of IPC-TM-650 2.4.24 49/244 45/232 47/250 44/240 56/231 59/245 thermal expansion (α1/α2), ppm/ ° C. water PCT/121° C./1 hr 0.30 0.31 0.33 0.32 0.34 0.31 absorption 288° C. Dip288° C. >600 >600 >600 >600 >600 >600 thermal resistance Dk(2-10 GHz) Cavity 3.95 3.94 3.96 3.9 3.91 3.41 Df(2-10 GHz) Cavity 0.0041 0.0045 0.0046 0.0042 0.0041 0.0026 flammability UL94 V-0 V-0 V-0 V-0 V-0 V-0

Liquid crystal polymers generally exhibit good chemical, moisture and temperature resistance, and good mechanical strength, and can be formed into thin films that have a high degree of structural integrity. However, the cost and/or the dielectric constant of a film made solely of LCP may be too high for certain electronic applications.

The liquid crystal polymer according to the present invention is selected from a liquid crystalline polymer (or a thermoplastic polymer capable of forming an optically anisotropic melt phase) processable in a molten state. Chemical formulation of the liquid crystal polymer is not particularly limited to a specific one as long as it is a liquid crystalline polymer that can be melt-processable, and examples thereof may include a thermoplastic liquid crystal polymer of vinyl type, a thermoplastic liquid crystal aromatic polyamide, or a thermoplastic liquid crystal aromatic polyester, and preferably, modified by introducing allyl group at terminals and/or side ends thereto. The liquid crystal polymer of the present invention can carry out free radical reaction to form an interpenetrating polymer network by the allyl group. In Table 1-2, Example 13 uses low Dk glass fiber, and Example 8 and Example 9 use E-glass fiber.

The thermoplastic liquid crystal polymer of vinyl type has the following structure:

The thermoplastic liquid crystal aromatic polyamide has the following structure:

The liquid crystal polymer of the present invention has FTIR spectrum shown as the FIGURE Peak 3472 cm⁻¹ relates to —OH or —NH stretch. Peak 3097 cm⁻¹ relates to Vinyl or —CH2 asymmetric stretch. Peaks 2950 cm−1, 2919−1 cm, 2874 cm−1 and 2842 cm−1 relate to —C≡C—H, —C═CH2, —C—CH3 or

Peaks 1730 cm−1 and 1715 cm−1 relate to aromatic ester, C═O stretch, saturated C═O stretch or aromatic C═O. Peaks 1640 cm−1 and 1605 cm−1 relate to —C═C or ring mode C═C. Peaks 1640 cm−1, 1570 cm−1 and 1482 cm−1 relate to —NH bending or asymmetric

stretch. Peaks 1459 cm−1 and 1377 cm−1 relate to

symmetric stretch. Peaks 1299 cm−1, 1244 cm−1, 1188 cm−1, 1153 cm−1, 1043 cm−1 and 1023 cm−1 relate to —C—O—, —C—O—C— or —C—C—C—. Peaks 1377 cm−1 to 1023 cm−1 relate to amide, imide, —CN stretch. Peaks 827 cm−1 to 691 cm−1 relate to —C═C— on benzene ring, para or meta substituted phenyl or —NH out of plane wagging or mono. It can be found from the FIGURE that peaks identify the thermoplastic liquid crystal polymer of vinyl type and the thermoplastic liquid crystal aromatic polyamide.

TABLE 2 INFLUENCE OF BMI RESIN SPECIES AND AMOUNT BMI RESIN EXAMPLE 4-2 A1 A2 A3 A4 A5 A6 A7 A8 PPE resin SA9000 42.5 40 37.5 35 32.5 37.5 37.5 37.5 BMI resin 2300 0 0 0 0 0 0 15 0 4000 0 0 0 0 0 15 0 0 5100 5 10 15 20 25 0 0 0 TMH 0 0 0 0 0 0 0 15 Polybutadiene Ricon100 10 10 10 10 10 10 10 10 Crosslinking TAIC 42.5 40 37.5 35 32.5 37.5 37.5 37.5 agents Flame XP7866, 20 20 20 20 20 20 20 20 retardants phr fillers Fused 20 20 20 20 20 20 20 20 silica, phr catalysts Peroxide 2.5 2.5 2.5 2.5 2.5 2.5 2.5 2.5 119° C. for a half life of 10 hrs Tg, TMA IPC-TM- 210 212 212 211 211 212 222 195 650 2.4.24.3 Coefficient IPC-TM- 60/296 58/250 56/211 54/207 50/197 55/260 45/170 45/288 of 650 thermal 2.4.24 expansion (α1/α2), ppm/° C. water PCT/121° C./ 0.30 0.34 0.39 0.44 0.46 0.41 0.47 0.33 absorption 1 hr 288° C. Dip288° C. >600 >600 >600 >600 >600 >600 >600 >600 thermal resistance Dk(2-10 GHz) Cavity 3.85 3.87 3.90 3.94 3.98 3.91 3.93 3.86 Df(2-10 GHz) Cavity 0.0040 0.0041 0.0040 0.0042 0.0043 0.0042 0.0046 0.0041 flammability UL94 V-0 V-0 V-0 V-0 V-0 V-1 V-0 V-0 BMI RESIN Comparative EXAMPLE 4-2 A9 A10 A11 A12 A13 A14 A15 example PPE resin SA9000 37 37 37 37 37 37.5 37 50 BMI resin 2300 8 0 8 0 0 5 4 0 4000 8 8 0 8 0 5 4 0 5100 0 8 0 0 8 5 4 0 TMH 0 0 8 8 8 0 4 0 Polybutadiene Ricon 10 10 10 10 10 10 10 0 100 Crosslinking TAIC 37 37 37 37 37 37.5 37 50 agents Flame XP7866, 20 20 20 20 20 20 20 20 retardants phr fillers Fused 20 20 20 20 20 20 20 20 silica, phr catalysts Peroxide 2.5 2.5 2.5 2.5 2.5 2.5 2.5 2.5 119° C. for a half life of 10 hrs Tg, TMA IPC-TM- 208 204 205 200 214 210 207 218 650 2.4.24.3 Coefficient IPC-TM- 50/210 57/278 45/230 52/268 54/290 53/240 49/225 64/325 of 650 thermal 2.4.24 expansion (α1/α2), ppm/° C. water PCT/121° C./ 0.43 0.42 0.41 0.36 0.44 0.40 0.39 0.33 absorption 1 hr 288° C. Dip288° C. >600 >600 >600 >600 >600 >600 >600 >600 thermal resistance Dk(2-10 GHz) Cavity 3.96 3.91 3.90 3.87 3.89 3.91 3.90 3.80 Df(2-10 GHz) Cavity 0.0041 0.0041 0.0045 0.004 0.0039 0.0041 0.0043 0.0044 flammability UL94 V-0 V-0 V-0 V-0 V-0 V-0 V-0 V-0

The coefficient of thermal expansion was measured with different species and amount of BMI resin. The more the amount of BMI resin is, the lower the coefficient of thermal expansion is. In the example, there are three kinds of comparison comprising three groups that A1-A5 shows different amount of BMI with the same species, A6-A8 shows the same amount of BMI with different species and A9-A15 shows about the same total amount of BMI with more than two species. In Table 2, part numbers 2300, 4000, 5100 and TMH of BMI are produced by Daiwakasei Industry CO., LTD, in which part number 2300 has chemical name of phenyl methane maleimide, part number 4000 has chemical name of 2,2′-bis[4-(4-maleimidophenoxy)phenyl]propane, part number 5100 has chemical name of 3,3′-dimethyl-5,5′-diethyl-4,4′-diphenylmethane bismaleimide and part number TMH has chemical name of 1,6′-bismaleimide-(2,2,4-trimethyl)hexane.

It can be found from group A1-A5 that by increasing the amount of BMI resin, the thermal expansion coefficient would decrease. However, by increasing the amount of BMI resin, the water absorption would also increase. As to group A6-A8, different BMI resins may reduce the thermal expansion coefficient, but would also affect the water absorption. Regarding group A9-A15, different combination of BMI resins may reduce the thermal expansion coefficient, and affect the water absorption also. In the invention, the object of addition of BMI to the dielectric material is to reduce the thermal expansion coefficient. However, the more the amount of BMI resin is, the higher the water absorption is. Therefore, the polymer additives are added to reduce the water absorption.

TABLE 3 INFLUENCE OF POLYMER ADDITIVES SPECIES AND AMOUNT POLYMER ADDITIVES EXAMPLE 4-3 B1 B2 B3 B4 B5 B6 B7 PPE resin SA9000 40 37.5 35 32.5 30 37.5 37.5 BMI resin 5100 15 15 15 15 15 15 15 Polybutadiene Ricon100 5 10 15 20 25 0 0 Ricon130MA8 0 0 0 0 0 10 0 Ricon150 0 0 0 0 0 0 10 Ricon257 0 0 0 0 0 0 0 SMA S:M = 3:1 0 0 0 0 0 0 0 S:M = 4:1 0 0 0 0 0 0 0 S:M = 5:1 0 0 0 0 0 0 0 S:M = 6:1 0 0 0 0 0 0 0 S:M = 8:1 0 0 0 0 0 0 0 Crosslinking TAIC 40 37.5 35 32.5 30 37.5 37.5 agents Flame retardant XP7866, phr 20 20 20 20 20 20 20 Fillers Fused silica, phr 20 20 20 20 20 20 20 catalysts Peroxide 119° C. 2.5 2.5 2.5 2.5 2.5 2.5 2.5 for a half life of 10 hrs Tg, TMA IPC-TM-650 221 212 200 194 186 213 217 2.4.24.3 coefficient of IPC-TM-650 53/201 56/211 64/220 67/260 74/300 58/265 57/270 thermal expansion 2.4.24 (α1/α2), ppm/° C. water absorption PCT/121° C./1 hr 0.43 0.39 0.35 0.32 0.28 0.45 0.43 288° C. thermal Dip288° C. >600 >600 >600 >600 >600 >600 >600 resistance Dk(2-10 GHz) Cavity 3.93 3.90 3.87 3.86 3.84 3.92 3.90 Df(2-10 GHz) Cavity 0.0043 0.0040 0.0041 0.0040 0.0039 0.0045 0.0044 flammability UL94 V-0 V-0 V-0 V-1 V-1 V-0 V-0 POLYMER ADDITIVES Comparative EXAMPLE 4-3 B9 B10 B11 B12 B13 example PPE resin SA9000 37.5 37.5 37.5 37.5 37.5 42.5 BMI resin 5100 15 15 15 15 15 15 Polybutadiene Ricon100 0 0 0 0 0 0 Ricon130MA8 0 0 0 0 0 0 Ricon150 0 0 0 0 0 0 Ricon257 0 0 0 0 0 0 SMA S:M = 3:1 10 0 0 0 0 0 S:M = 4:1 0 10 0 0 0 0 S:M = 5:1 0 0 10 0 0 0 S:M = 6:1 0 0 0 10 0 0 S:M = 8:1 0 0 0 0 10 0 Crosslinking agents TAIC 37.5 37.5 37.5 37.5 37.5 42.5 Flame retardants XP7866, phr 20 20 20 20 20 20 fillers Fused silica, phr 20 20 20 20 20 20 catalysts Peroxide 119° C. 2.5 2.5 2.5 2.5 2.5 2.5 for a half life of 10 hrs Tg, TMA IPC-TM-650 220 215 210 206 195 222 2.4.24.3 coefficient of IPC-TM-650 45/232 48/237 50/245 51/240 53/260 45/200 thermal expansion 2.4.24 (α1/α2), ppm/° C. water absorption PCT/121° C./1 hr 0.46 0.45 0.43 0.43 0.40 0.56 288° C. thermal Dip288° C. >600 >600 >600 >600 >600 >600 resistance Dk(2-10 GHz) Cavity 3.95 3.95 3.93 3.91 3.90 3.93 Df(2-10 GHz) Cavity 0.0085 0.0073 0.0064 0.0056 0.0042 0.0043 flammability UL94 V-0 V-0 V-0 V-0 V-0 V-0

The water absorption was measured with different species and amount of polymer additives. Polybutadiene (PB) and styrene-maleic anhydride (SMA) were used as the polymer additives in the invention. It can be found from using the different amount of PB with the same species that by increasing the amount of PB, the water absorption would decrease. However, with the increasing amount of PB, the coefficient of thermal expansion would also increase. As to using different species of PB in combination with SMA, it shows SMA can reduce the water absorption and the coefficient of thermal expansion, but Df may remain high. However, PB can be used to reduce Df In Table 3, part numbers Ricon100, Ricon130MA8, Ricon150 and Ricon257 of PB are produced by Sartomer CO., LTD, in which part number Ricon100 has chemical name of butadiene styrene copolymer, part number Ricon130MA8 has chemical name of butadiene adducted with maleic anhydride, part number Ricon 150 has chemical name of polybutadiene resin and Ricon 257 has chemical name of polybutadiene grafted with styrene and benzene in toluene solution. In Table 3, SMA with S:M=3:1 indicates that the ratio of styrene to maleic anhydride is 3 to 1. Generally, the ratios are about 1:1˜12:1.

TABLE 4 INFLUENCE OF DIFFERENT SPECIES OF CROSSLINKING AGENTS CROSSLINKING AGENT EXAMPLE 4-4 D1 D2 D3 D4 D5 PPE resin SA9000 37.5 37.5 37.5 37.5 37.5 BMI resin 5100 15 15 15 15 15 polybutadiene Ricon100 10 10 10 10 10 Crosslinking TAC 37.5 0 0 0 0 agents TAIC 0 37.5 0 0 0 TBS 0 0 37.5 0 0 TMAIC 0 0 0 37.5 37.5 Flame retardants XP7866, phr 20 20 20 0 0 Decabromodiphenyl 0 0 0 10 0 Ethane, phr HCA derivative (II), 0 0 0 0 20 phr fillers Fused silica, phr 20 20 20 20 20 catalysts Peroxide 119° C. for 2.5 2.5 2.5 4 4 a half life of 10 hrs Tg, TMA IPC-TM-650 183 212 202 188 183 2.4.24.3 coefficient of IPC-TM-650 2.4.24 59/273 56/211 50/250 49/267 50/235 thermal expansion (α1/α2), ppm/° C. water absorption PCT/121° C./1 hr 0.39 0.39 0.12 0.35 0.30 288° C. thermal Dip288° C. >600 >600 >600 >600 >600 resistance Dk(2-10 GHz) Cavity 3.95 3.90 3.75 3.86 3.91 Df(2-10 GHz) Cavity 0.0039 0.0040 0.0035 0.004 0.0038 flammability UL94 V-0 V-0 V-0 V-0 V-0

The dielectric material of the invention may comprise at least one crosslinking agent with 40-80 parts by weight selected from the following groups consisting of Triallyl cyanurate (TAC), Triallyl isocyanurate (TAIC), 4-tert-butylstyrene and TMAIC. The properties of a copper-clad laminate with the dielectric material of the invention were measured with different species of crosslinking agents. It can be found by using TAC that Tg and the coefficient of thermal expansion were poor, and water absorption, Dk and Df were of ordinary level. As to TAIC, all the properties of a copper-clad laminate with the dielectric material of the invention were of ordinary level. However, one drawback with TAIC is that it is volatile during hot press cycle. The use of TMAIC can effectively improve the high volatility of TAIC because TMAIC has a high melting point and does not evaporated easily, while maintaining the properties to its ordinary level. Regarding 4-tert-butylstyrene, the coefficient of thermal expansion, water absorption and Df were excellent, but Dk is low.

TABLE 5 INFLUENCE OF DIFFERENT SPECIES OF FLAME RETARDANTS FLAME RETARDANTS EXAMPLE 4-5 E1 E2 E3 E4 E5 E6 PPE resin SA9000 37.5 37.5 37.5 37.5 37.5 37.5 BMI resin 5100 15 15 15 15 15 15 polybutadiene Ricon100 10 10 10 10 10 10 Crosslinking TAIC 37.5 37.5 37.5 37.5 37.5 37.5 agents Flame Decabromodiphenyl 10 0 0 0 0 0 retardants Ethane, phr XP7866, phr 0 20 15 10 0 0 Tetrakis(2,6-dimethylphenyl) 0 0 5 10 0 0 1,3-phenylene bisphosphate, phr HCA derivative (II), phr 0 0 0 0 20 0 DPO, phr 0 0 0 0 0 20 fillers Fused silica, phr 20 20 20 20 20 20 catalysts Peroxide 119° C. for a half 2.5 2.5 2.5 2.5 2.5 2.5 life of 10 hrs Tg, TMA IPC-TM-650 2.4.24.3 224 212 226 180 214 224 coefficient of IPC-TM-650 2.4.24 55/233 56/211 65/267 67/339 50/210 45/170 thermal expansion (α1/α2), ppm/ ° C. water PCT/121° C./1 hr 0.43 0.39 0.37 0.30 0.36 0.25 absorption 288° C. thermal Dip288° C. >60 >600 >600 >600 >600 >600 resistance Dk(2-10 GHz) Cavity 3.83 3.90 3.87 3.85 3.89 3.88 Df(2-10 GHz) Cavity 0.0043 0.0040 0.0040 0.0037 0.0036 0.0038 flammability UL94 V-0 V-0 V-0 V-0 V-0 V-0

If desired, the dielectric material of the invention may optionally comprise flame retardants. A halogen-containing flame retardant of decabromodiphenyl ethane with 7-15 phr based on the total weight of PPE, BMI, polymer additives and crosslinking agents may be added to the dielectric material of the invention. The dielectric material of the invention may comprise at least one flame retardant without halogen with 12-14 phr based on the total weight of PPE, BMI, polymer additives and crosslinking agents selected from the following groups consisting of phosphor-containing flame retardants and phosphates. The phosphor-containing flame retardants and phosphates are produced by ALBEMARLE CO., LTD, wherein HCA derivative (III) having product name of XP7866 comprises organic fillers, 10-15% phosphor. XP7866 has a particle size in a range of 0.5 μm-60 μm. The phosphates are like tetrakis(2,6-dimethylphenyl) 1,3-phenylene bisphosphate.

TABLE 6 INFLUENCE OF DIFFERENT SPECIES OF FILLERS FILLERS EXAMPLES 4-6 F1 F2 F3 F4 F5 F6 F7 PPE resin SA9000 37.5 37.5 37.5 37.5 37.5 37.5 37.5 BMI resin 5100 15 15 15 15 15 15 15 polybutadiene Ricon100 10 10 10 10 10 10 10 Crosslinking TAIC 37.5 37.5 37.5 37.5 37.5 37.5 37.5 agents Flame XP7866, phr 20 20 20 20 20 20 20 retardants fillers Fused silica, 0 20 10 10 30 25 45 phr Siliesoft, phr 0 0 0 0 0 0 0 Ball type 20 0 10 0 0 0 0 silica catalysts Peroxide 2.5 2.5 2.5 2.5 2.5 2.5 2.5 119° C. for a half life of 10 hrs Tg, TMA IPC-TM-650 210 212 214 220 208 215 195 2.4.24.3 coefficient of IPC-TM-650 53/220 56/211 52/225 58/260 45/210 50/220 40/205 thermal 2.4.24 expansion (α1/α2), ppm/ ° C. water PCT/121° C./ 0.41 0.39 0.40 0.39 0.38 0.40 0.36 absorption 1 hr 288° C. thermal Dip288° C. >600 >600 >600 >600 >600 >600 >600 resistance Dk(2-10 GHz) Cavity 3.87 3.90 3.88 3.85 3.96 4.01 4.06 Df(2-10 GHz) Cavity 0.0039 0.0040 0.0040 0.0040 0.0041 0.0043 0.0045 flammability UL94 V-0 V-0 V-0 V-0 V-0 V-0 V-0 Frequency of Drill holes 500 300 400 — — — — changing drill count bit FILLERS EXAMPLES 4-6 F8 F9 PPE resin SA9000 37.5 37.5 BMI resin 5100 15 15 polybutadiene Ricon100 10 10 Crosslinking agents TAIC 37.5 37.5 Flame retardants XP7866, phr 20 20 Fillers Fused silica, phr 0 0 Siliesoft, phr 10 20 Ball type silica, phr 10 0 catalysts Peroxide 119° C. for a half life 2.5 2.5 of 10 hrs Tg, TMA IPC-TM-650 2.4.24.3 206 210 coefficient of thermal expansion IPC-TM-650 2.4.24 50/217 51/222 (α1/α2), ppm/° C. water absorption PCT/121° C./1 hr 0.36 0.40 288° C. thermal resistance Dip288° C. >600 >600 Dk(2-10 GHz) Cavity 3.90 3.95 Df(2-10 GHz) Cavity 0.0053 0.0060 flammability UL94 V-0 V-0 Frequency of changing drill bit Drill holes count 600 800

The low dielectric material of the invention may optionally comprise fillers. The suitable fillers such as fused silica, sphere-shaped silica and soft silica, e.g., siliesoft may be used, wherein the soft silica can be used to reduce a drill bit wearing away when PCB is drilled to form holes by the drill bit, comparing Examples F1-F3 with Examples F8-F9. The soft silica has a particle size in a range of 0.5 μm-10 μm. The suitable amount of filler is 8-50 phr based on the total weight of PPE, BMI, polymer additives and crosslinking agents. It can be found from the fused silica and the sphere-shaped silica with the same amount that the sphere-shaped silica has lower Dk and Df than the fused silica.

TABLE 7 INFLUENCE OF DIFFERENT AMOUNT AND SPECIES OF CATALYSTS CATALYSTS EXAMPLE 4-7 G1 G2 G3 G4 PPE resin SA9000 37.5 37.5 37.5 37.5 BMI resin 5100 15 15 15 15 polybutadiene Ricon100 10 10 10 10 Crosslinking TAIC 37.5 37.5 37.5 37.5 agents Flame XP7866, phr 20 20 20 20 retardants fillers Ball type silica 20 20 20 20 catalysts Peroxide 116° C. for a 0 0 0 0 half life of 10 hrs Peroxide 119° C. for a 2.5 3 7 8 half life of 10 hrs Peroxide 128° C. for a 0 0 0 0 half life of 10 hrs Tg, TMA IPC-TM-650 2.4.24.3 212 220 222 227 coefficient of IPC-TM-650 2.4.24 56/211 53/225 49/220 50/180 thermal expansion (α1/α2), ppm/ ° C. water PCT/121° C./1 hr 0.39 0.43 0.47 0.60 absorption 288° C. thermal Dip288° C. >600 >600 >600 >600 resistance Dk(2-10 GHz) Cavity 3.90 3.91 3.90 3.96 Df(2-10 GHz) Cavity 0.0040 0.0042 0.0045 0.0049 flammability UL94 V-0 V-0 V-0 V-0 CATALYSTS EXAMPLE 4-7 G5 G6 G7 G8 G9 PPE resin SA9000 37.5 37.5 37.5 37.5 37.5 BMI resin 5100 15 15 15 15 15 polybutadiene Ricon100 10 10 10 10 10 Crosslinking TAIC 37.5 37.5 37.5 37.5 37.5 agents Flame XP7866, phr 20 13 13 13 13 retardants fillers Ball type silica 20 13 13 13 13 catalysts Peroxide 116° C. for a 2.5 0 1.5 1.5 1 half life of 10 hrs Peroxide 119° C. for a 0 0 0 1.5 1 half life of 10 hrs Peroxide 128° C. for a 0 2.5 1.5 0 1 half life of 10 hrs Tg, TMA IPC-TM-650 2.4.24.3 208 225 220 209 215 coefficient of IPC-TM-650 2.4.24 57/230 50/230 47/226 52/220 50/235 thermal expansion (α1/α2), ppm/ ° C. water PCT/121° C./1 hr 0.42 0.38 0.40 0.42 0.38 absorption 288° C. thermal Dip288° C. >600 >600 >600 >600 >600 resistance Dk(2-10 GHz) Cavity 3.88 3.91 3.92 3.93 3.91 Df(2-10 GHz) Cavity 0.0039 0.0040 0.0041 0.0042 0.0039 flammability UL94 V-0 V-0 V-0 V-0 V-0

The low dielectric material of the invention may optionally comprise catalysts including peroxides having 116° C.-128° C. for a half life of 10 hours. The suitable amount of peroxide is 2-8 phr based on the total weight of PPE, BMI, polymer additives and crosslinking agents. The preferable catalyst is a peroxide having 119° C. for a half life of 10 hours.

The low dielectric material of the invention may comprise PPE, but not comprise epoxy resin. The desired values of Dk and/or Df cannot be obtained, if epoxy resin is added to the dielectric material of the invention. When reacting epoxy resin with the dielectric material of the invention, the open rings of the epoxy resin may produce excess OH groups, therefore causing the Dk and Df value to remain high and unable to decrease. 

What is claimed is:
 1. A low dielectric material comprising: (i) 5-50 parts by weight of polyphenylene ether (PPE) resin having a Mw of 1000-7000, a Mn of 1000-4000 and Mw/Mn=1.0-1.8; wherein polyphenylene ether resin is represented by the formula

wherein Y represents at least one C, O and benzene ring or the combination; and (ii) 10-90 parts by weight of liquid crystal polymer with allyl group having a Mw of 1000-5000, a Mn of 1000-4000 and Mw/Mn=1.0-1.8, wherein the dielectric material has Dk of 3.4-4.0 and Df of 0.0025-0.0050.
 2. The low dielectric material of claim 1, further comprising 0.01-15 parts by weight of bismaleimide resins.
 3. The low dielectric material of claim 1, further comprising 0.01-10 parts by weight of polymer additives.
 4. The low dielectric material of claim 2, wherein the bismaleimide resins are selected from groups consisting of phenylmethane maleimide

wherein n≧1; bisphenol A diphenyl ether bismaleimide

3,3′-dimethyl-5,5′-diethyl-4,4′-diphenylethane bismaleimide

 and 1,6-bismaleimide-(2,2,4-trimethyl)hexane


5. The low dielectric material of claim 3, wherein the polymer additives are selected from groups consisting of homopolymers of butadiene

wherein y=70% and x+z=30%; random copolymers of butadiene and styrene

wherein y=30%, x+z=70% and w=≧1, and the amount of styrene=25 wt %; maleinized polybutadiene

wherein y=28% and x+z=72%, the amount of maleic anhydride=8 wt %; butadiene-styrene-divinylbenzene copolymer; and styrene maleic anhydride copolymer

wherein X=1-8 and n≧1.
 6. The low dielectric material of claim 1, further comprising at least one crosslinking agent with 40-80 parts by weight selected from the following groups consisting of


7. The low dielectric material of claim 1, further comprising catalysts including at least one peroxide having 116° C.-128° C. for a half life of 10 hours.
 8. The low dielectric material of claim 7, wherein the catalysts including at least one peroxide selected from groups consisting of dicumyl peroxide, α,α′-bis(tert-butylperoxy) diisopropyl benzene and 2,5-di(tert-butylperoxy)-2,5-dimethyl-3-hexyne.
 9. The low dielectric material of claim 1, further comprising fillers selected from groups consisting of fused silica, sphere-shaped silica, talc, aluminum silicate and soft silica.
 10. The low dielectric material of claim 9, wherein the soft silica has a particle size in a range of 0.5 μm-10 μm.
 11. The low dielectric material of claim 1, further comprising at least one flame retardant without halogen selected from the following groups consisting of phosphor-containing flame retardants and phosphates.
 12. The low dielectric material of claim 11, wherein the phosphor-containing flame retardants are selected from groups consisting of HCA derivative (I), HCA derivative (II) and HCA derivative (III), HCA derivative (I) having the following paradiphenyl phosphoryl dibenzyl structure:

HCA derivative (II) having the following structure:

wherein with the proviso that when B is —CH₂—, —CH(CH₃)—, m is 1 and n is 1 to 3; with the proviso that when B is ═CHCH═, m=2 and n=0; and HCA derivative (III) having the following structure:

wherein A is a direct bond, C₆-C₁₂ aryl, C₃-C₁₂ cycloalkyl, or a C₃-C₁₂cycloalkenyl, wherein said cycloalkyl or cycloalkenyl may be optionally substituted by a C₁-C₆ alkyl; each R¹, R², R³ and R⁴ are independently hydrogen, C₁-C₁₅ alkyl, C₆-C₁₂aryl, C₇-C₁₅ aralkyl or C₇-C₁₅ alkaryl; or R¹ and R² or R³ and R⁴ taken together can form a saturated or unsaturated cyclic ring, wherein said saturated or unsaturated cyclic ring may be optional substituted by a C₁-C₆ alkyl; each m is independently 1, 2, 3 or 4 each R⁵ and R⁶ are independently hydrogen or a C₁-C₆ alkyl; each n is independently 0, 1, 2, 3, 4 or 5; with the proviso that when A is aryl or a direct bond, n cannot be
 0. 